Gaseous combustion in electric discharges. Part IV.-The effect of moisture upon the cathodic combustion of carbonic oxide detonating gas

Abstract

It has been shown previously in part III of the present series that the combustion of carbonic oxide "detonating gas" is determined by a prior ionisation of both constituent gases ; and further that, whereas carbonic oxide can be and is burnt directly by oxygen in the absence of, and therefore without the intervention of, either moisture or metal atoms, the presence of such metal atoms sputtered from the cathode by the passage of the discharge actively promotes cathodic combustion by the overcoming of the electrostatic forces of repulsion existing between similarly charged ions of carbonic oxide and oxygen. It has shown by Bone and his co-workers that, though the rigidly dried "detonating gas" can be ignited, provided a sufficiently powerful condenser discharge be employed, and is then capable of propagating flame, (though combustion may be incomplete), the presence of even a minute quantity of steam not only renders the mixture much more readily ignitable, but also increases the velocity of flame propagation and ensures practically complete combustion. Hitherto, however, experiments have afforded but little direct evidence as to the precise nature of the mechanism of the rôle played by moisture in promoting combustion, and the present work was carried out with the object of attempting to throw some light upon this question. For this purpose the investigation has been confined to an experimental study of the combustion of the moist "detonating gas" in the cathode zone of a direct current discharge, because, as has been previously shown, the conditions can then be easily and accurately controlled over a considerable range without then be easily and accurately controlled over a considerable range without introducing disturbing phenomena, such as heat and catalytic action, which might otherwise tend to obscure the real issues. In the experiments described herein we have succeeded in realising conditions in which the ratio of the rate of combustion of the "detonating gas" containing a given partial pressure of steam, to the current passed by the discharge, is, in the absence of sputtered metal atoms, proportional to the number of steam molecules, and hence electrically charged steam molecules, within the cathode zone.